1. Technical Field
The present invention relates to an ink composition for inkjet recording, an inkjet recording method, and printed matter.
2. Background Art
Inkjet printers are widely used due to their advantages such as low noise and low running costs, and many printers capable of printing color images on plain paper are now widely available on market. However, it is extremely difficult to satisfy all the properties required of images produced using such printers, such as good color reproducibility, abrasion resistance, durability, light resistance, drying property, feathering, color bleed, duplex printing, and ink discharging stability. As a result, the ink used is selected based on the particular application.
In general, the ink used in inkjet recording is mainly composed of water, with a coloring agent and a wetting agent such as glycerin added to prevent clogging. As the coloring agent, dyes are widely used for their coloring and stability. However, the light resistance and water resistance of images produced using such dye-based ink are inferior. The water resistance can be improved in some degree by using specialized recording media having an ink absorbing layer, but is not satisfactory at all when it comes to plain paper.
To compensate for such defects, ink using a pigment has begun to be widely used as a coloring agent. Although pigment ink is successful and superior to dye ink with regard to light resistance, water resistance, etc., coloring is degraded by coherence of light having difference wavelengths and phases produced by multiple reflections of light within the pigment. Therefore, pigment ink is inferior to dye ink in general with regard to the coloring. In particular, the pigment ink used as ink for inkjet recording causes problems of deterioration of coloring (saturation) on plain paper and of gloss on specialized paper.
In an attempt to compensate for such degradation of coloring of the pigment ink, pigment particulates that are coated with resin are used. According to this method, the fixing and the gas resistance properties of the ink are further improved by the resin, and in addition dispersion is greatly stabilized. However, currently, pigment ink is not still on a par with dye ink with regard to gloss.
JP-2007-169359-A discloses using a quinacridone-based pigment liquid dispersion while limiting the ratio Z/Y of the two absorption peaks Y and Z to a range of from 0.94 to 1.21 to obtain good coloring. JP-2007-238808-A discloses regulating the ratio of the two absorption peaks Y and Z of C.I. Pigment Red 122 to a range of from 0.85 to 1.00 to obtain good coloring. Although these are successful in some degree, just adjusting the range of Z/Y does not lead to improvement of gloss so that the problem about the coloring on specialized gloss paper or coated paper remains unsolved.